1. Field
The present disclosure relates to an image forming apparatus that controls a transfer power for transferring an image formed on a photosensitive medium onto a transfer medium.
2. Description of the Related Art
In image forming apparatuses, a process of forming an image on a print medium is performed as follows. First, a photosensitive medium is exposed to light, thereby forming an electrostatic latent image thereon and a developing agent is then provided to the electrostatic latent image to develop the image. In other words, particles of the developing agent that are charged on a surface of the photosensitive medium are distributed according to the type of electrostatic latent image. Then, the image formed on the photosensitive medium is transferred onto a print medium. That is, the particles of the developing agent on the surface of the photosensitive medium are transferred onto the print medium. Lastly, the developing agent transferred onto the print medium is heated and pressured to be fixed thereon, thereby completing the formation of an image.
Among the above-described processes, the process of transferring the image formed on the photosensitive medium onto a print medium will now be described in more detail. The image formed on the photosensitive medium may be directly transferred onto a print medium on which an image is to be finally formed, e.g., paper or may be first transferred onto an intermediate transfer medium and then secondarily transferred onto a print medium from the intermediate transfer medium. Hereinafter, all the objects onto which an image is transferred are referred to as a transfer medium. When a voltage having a polarity that is opposite to that of charged particles of a developing agent on a surface of a photosensitive medium or an intermediate transfer medium is applied to a transfer medium, the particles of the developing agent are transferred onto the transfer medium by an electrostatic force. For example, if a positive voltage is applied to an opposite side of the photosensitive medium or the intermediate transfer medium with respect to the transfer medium when particles of a developing agent on a surface of a photosensitive medium or an intermediate transfer medium which are to form an image are negatively charged, the particles of the developing agent are transferred onto a surface of the transfer medium by an electrostatic force.
In this regard, the voltage may be applied to the opposite side of the transfer medium by a constant current (CC) method or constant voltage (CV) method. The former is a method whereby a CC is applied to a transfer member of a transfer roller positioned on an opposite side of a transfer medium and the latter is a method whereby a CV is applied thereto. In particular, when the CC method is used, an image forming apparatus is capable of appropriately responding to longitudinal changes such as a change in a load of a total system and a change in a resistance of a transfer medium, while it is difficult to respond to temporary changes such as a change in the density of images in consideration of characteristics in which a voltage changes according to a change in resistance. In contrast, when the CV method is used, a constant voltage is maintained in spite of frequent small changes in resistance and thus it is possible to appropriately respond to temporary resistance changes, while it is difficult to appropriately respond to longitudinal resistance changes.